During the fall 1993 semester, Argos Space Endeavours (ASE), in cooperation with the University Space Research Association (USRA), NASA Š Johnson Space Center (JSC), and the University of Texas Department of Aerospace Engineering completed a preliminary design of Project Aeneas, a robotic exploration mission to both Mars and Phobos.

The beginning of this final report discusses the project objectives and provides a summary of the Aeneas mission. Subsequent sections provide detailed explanations of the various elements of Project Aeneas developed by ASE including science, spacecraft, probes, and orbits and trajectories. The report concludes by describing the management procedures and project costs.

Project Objectives

Three main objectives drive the design of Project Aeneas. First, the mission must provide data to aid in determining a site on Mars suitable for a piloted landing. ASE proposes to achieve this objective through remote sensing of Mars, followed by the deployment of probes to the Martian surface, verifying the remote sensing data. To further aid the site selection process, Project Aeneas includes an investigation of the surface geology and weather patterns on Mars through the use of additional surface probes and penetrators.

The second objective given to ASE includes proving the concept of producing fuel on Mars from primarily indigenous materials. ASE addresses this concept, termed In-Situ Resource Utilization (ISRU), by collecting carbon-dioxide from the Martian atmosphere, adding hydrogen brought from Earth, and, after heating, producing methane through a process known as the Sabatier reaction.

A third and final objective of Project Aeneas is the analysis of the composition of the Martian moon Phobos. Project Aeneas design includes a penetrator device, targeted at the crater Stickney on Phobos, to return data on the chemical and geological properties of the Martian moon.

Mission Summary

The entire Aeneas mission comprises three spacecraft, launched via two Soviet Proton rockets. The first launch will deliver one Mars orbiter and one Phobos probe delivery spacecraft. The launch of the second Proton will transport a second orbiter to Mars. Each of the orbiters contain remote sensing instruments, surface probes and penetrators, as well as an ISRU device. The Phobos probe delivery spacecraft carries the Phobos probe as well as additional remote sensing apparatus.

Science Element

The three main objectives of the Aeneas mission drive the science element of the project and are reiterated below:

Return data to Earth to aid in the determination of future piloted landing sites,

Prove the ISRU fuel production concept, and

Provide data to determine the composition of Phobos.

The science element suggests the following strategies to complete these objectives:

Remote sensing of Mars to compliment existing data,

Deployment of probes to the Martian surface,

Deployment of the ISRU test facility to Mars,

Remote sensing of Phobos, and

Deployment of probes to Phobos.

Three instruments compose the Mars remote sensing strategy of the science element: a Gamma Ray Spectrometer (GRS), a High Resolution Camera (HRC), and a Thermal Emission Spectrometer (TES). The GRS returns low resolution data on the elemental composition of the targeted surface. The HRC produces detailed images of possible landing sites, and the TES provides information on the temperature and dust loading of the Martian atmosphere. ASE selected these instruments based on the type of data returned by the instrument and by the mass, power, cost, and volume constraints on the Aeneas mission.

ASE selected seven different types of instruments for the probes of Project Aeneas. These instruments include a Seismicity Network (SEIS), an Atmospheric Structure Instrument (ASI), a Mossbauer Spectrometer (MBS), an Alpha Proton X-Ray Spectrometer (APXS), a Thermal Analysis/Evolved Gas Analyzer (TA/EGA), a Surface Imager (SI), and a Meteorology Network (MET). The SEIS returns data about the seismic nature of the Martian geology, while the ASI provides data on the altitude varying properties of the atmosphere. The MBS and APXS analyze respectively the iron compounds and elemental composition of a Martian soil sample. The actual compounds present in the soil are revealed by the TA/EGA, and the SI produces stereoscopic images of the surface. Lastly, the MET relays meteorological information such as wind speed and direction, temperature, particulate density, and humidity.

The Aeneas ISRU concept proposes to make methane from carbon-dioxide combined with onboard hydrogen, thus meeting the second objective of the element. Due to mass and power constraints, ASE proposes an ISRU design which collects, compresses, and heats a Martian atmospheric sample using the kinetic energy of the probe as it descends from orbit. This atmospheric sample, composed of 97% carbon-dioxide, once mixed with hydrogen and heated, produces methane and water through the Sabatier reaction shown below

Sensors in the Sabatier reactor will then detect the presence of methane, proving the concept of fuel production on Mars.

To fulfill the last science objective, the ASE science element uses a similar remote sensing and probes approach. Remote sensing of Phobos will be accomplished via a GRS unit, similar to the GRS on the Mars orbiter. Project Aeneas also includes the deployment of two probes to the surface of Phobos. One probe will target the crater Stickney on Phobos, providing the probe with increased access to the interior of Phobos. The ejecta found inside and near Stickney may also yield important information about the composition and geology of Phobos. The second probe adds redundancy to the Phobos mission and incorporates the flexibility to analyze an additional site.

Spacecraft Element

In order to provide redundancy and avoid a single catastrophic failure of Project Aeneas, ASE chose to launch three separate spacecraft, named Mars-Silva 1, 2, and 3, each containing different instrument packages. To simplify the design, the Common Spacecraft Bus (CSB) provides the structural base of each of the Mars-Silva spacecraft. Figure 1 is a drawing of the Mars-Silva spacecraft. The mass of each spacecraft is approximately 1100 kg, and all of the Mars-Silva units comprise an orbiter, a probe deployment module, and an R-40B engine. ASE estimates each spacecraft will cost under the $150 million budget for "discovery" class missions. ASE estimates the three spacecraft will cost approximately $400 million total.

Figure 1 Drawing of the Mars-Silva Spacecraft

Even though each spacecraft has approximately equal mass, the probe configurations of each Mars-Silva vehicle differ. Mars-Silva 1 will deliver five science penetrators, one ISRU probe, and one canister lander containing two micro-rovers. The Mars-Silva 2 vehicle carries two Comet Rendezvous Asteroid Flyby (CRAF) type penetrators for deployment to Phobos. Lastly, the Mars-Silva 3 spacecraft holds three science penetrators, one additional ISRU probe, and two canisters each delivering two micro-rovers.

Even though Project Aeneas calls for three spacecraft, only two launch vehicles will be necessary. A single Proton rocket will launch both Mars-Silva 1 and 2 simultaneously, yielding a total injected mass of approximately 2055 kg. An additional Proton will carry the 1150 kg Mars-Silva 3 vehicle. A D1e upper stage engine provides a C3L injected mass capability of 5400 kg for each launch vehicle. ASE estimates a total mission launch cost of $80 million.

The guidance, navigation, and control of the Mars-Silva spacecraft includes three-axis control mechanisms and guidance mechanisms. Specifically, momentum wheels will provide three-axis control, and thrusters will function as an outlet for momentum dumping. Guidance is provided by the CSB. The CSB contains horizon sensors for simple guidance measurements, gyroscopes for measurements requiring high-accuracy, and a star tracker to calibrate the gyroscopes.

The three Mars-Silva vehicles receive electrical power through two means: silicon solar cells, and NiH2 batteries. The deployable solar cells provide 190 W of power, enough power for all spacecraft operations. The NiH2 batteries produce only 51 W of power. The batteries provide power primarily during blackout periods of the spacecraft. Approximately 10,000 light/dark cycles are expected during the mission. During these periods, the batteries provide enough power to operate the attitude control system, computer, and either the communication system or one scientific instrument.

ASE determined that the Rockwell RI 1750A/B computer would satisfy the data management needs of the Mars-Silva spacecraft. This computer provides 1750 instruction set architecture, a 16-bit processor, 1.8 Mips throughput, and 3.9 megabytes of storage. The Rockwell computer requires 7 W of power and has a mass of 2.5 kg.

Probes Element

ASE defined three requirements for the probes to achieve a successful exploration of Mars:

Mars penetrators form the backbone of the Aeneas probe fleet. Figure 2 shows a typical Martian penetrator. Penetrators enter the atmosphere from orbit and deploy drag bodies to slow the probe to a safe impact velocity. On impact with the surface, the penetrator submerges approximately two-thirds of its length into the surface of the planet. Penetration of the surface allows for the collection of deep soil samples for analysis, and gives the probe a firm base for seismic measurements. Communications are relayed back to Earth via the orbiting Mars-Silva spacecraft.

Figure 2 Drawing of Martian Penetrator

Due to the absence of an atmosphere and a weak gravitational field at Phobos, the Aeneas Phobos probe utilizes CRAF-type, proximity operations techniques to navigate around and penetrate Phobos. After penetration, the mission of the Phobos probe is similar to that of the Mars penetrator; the Phobos probe analyzes samples from beneath the surface of Phobos for their chemical and geological characteristics. Mars-Silva 2 will deliver the Phobos probe and relay probe data back to Earth.

The Mars lander and micro-rover combination constitute the Martian surface operations for Project Aeneas. The primary function of the lander is delivery of the micro-rovers to the surface. The lander also relays communications from the micro-rovers to the Mars-Silva orbiter. Micro-rovers carry either a single APXS or MBS instrument. A micro-rover can travel approximately 20 meters per day, analyzing samples along its path.

Orbits and Trajectory Element

ASE adopted five design strategies in establishing the orbit and trajectory for the Aeneas mission:

To design a "typical" transfer trajectory to Mars,

Use Hohmann transfer data to carry out preliminary mission design,

To size the spacecraft using Hohmann data,

Use Lambert targeting to refine the initial trajectory calculations, and

To identify spacecraft and launch system requirements based on an optimized trajectory.

In the design of the Aeneas trajectory, ASE first calculated a Hohmann transfer trajectory, producing a time of flight of 258 days and a C3 of 8.6 km2/s2. Next, ASE optimized the Hohmann trajectory using Lambert targeting techniques. This included identifying launch opportunities and C3 requirements using "pork chop" plots, provided by the Jet Propulsion Laboratory (JPL). The orbits and trajectory element then optimized the trajectory for minimum launch C3, minimum arrival C3, and launch and arrival dates. Lastly, ASE identified booster and upper-stage combinations which satisfy the launch C3 and spacecraft mass requirements. The Lambert trajectory optimized for minimum launch C3 gave a time of flight of 202 days, and a launch C3 of 8.8 km2/s2. Figure 3 shows a plot of the Earth-Mars Lambert trajectory.

Figure 3 Plot of Earth-Mars Lambert Trajectory

The general scheme of orbit insertion follows three distinct paths. First, Mars-Silva 1 and 2 separate during the transfer trajectory. Next, Mars-Silva 1 inserts into a 60” inclination orbit about Mars. Mars-Silva 2 diverges into a near equatorial orbit, closer to the orbital plane of Phobos. When Mars-Silva 3 arrives, the spacecraft enters a 60” inclined orbit, similar to Mars-Silva 1.

The orbits for Mars-Silva 1 and 3 have a semi-major axis of 3880 km, an altitude of 483 km, an eccentricity of nearly zero, and an inclination of approximately 60”. This orbit gives coverage of ±60” latitude and requires 12 revolutions to obtain a near-repeat ground track. The orbiter should be able to completely map the surface in approximately one year.

Recommendations

The following list of recommendations are areas of Project Aeneas which require further development.

Develop the ISRU vehicle in detail (possibly a project that should be handled by ASE 363Q)

Develop the Penetrator structural design (possibly a project that should be handled by ASE 363Q)

Carry out a more in-depth analysis of the trajectory issues. In particular the targeting of the spacecraft into Mars orbits and the final form of the Mars orbits themselves.

Carry out a more in-depth analysis and design on the spacecraft and its subsystems. The work carried out by ASE is preliminary and is only intended to provide an overall spacecraft design which would be suitable for a mission like Project Aeneas.

Investigate the targeting issues involved in delivering probes to the surface of Mars and Phobos. In particular, develop a model for the thermal environment that the probes will encounter upon entering the Martian atmosphere. Also, develop guidance and control systems which will ensure that the probes are delivered accurately.

Carry out a detailed study on how the orbiters will map the surface of Mars in preparation for the deployment of probes. Generate ground tracks and figure out how (in terms of orbit design) to maximize the coverage of interested locations on the surface.

Consider adding studies of micro meteoroid impacts on the Martian surface and radiation levels during the cruise phase to Mars.